Lubricating composition



Patented Jan. 30,

LUBRICATING COMPOSITION William A. Zisman and Charles M. Murphy, Jr.,

Washington, D. Bethesda, Md.

and John K.

Wolfe,

No Drawing. Application February 3, 1945, Serial No. 576,106

(Granted under the act 0. March 3, 1883, as amended April 30, 1928; 3700. G. 757) 8 Claims.

Our invention relates to lubricating compositions and deals specificallywith the preparation of lubricants for the lubrication of bearingsurfaces in instruments such as watches, meters, gyro compasses, gunsights, bomb sights, and in high speed motors and similar movementswhere an extremely low coefficient of friction is essential.

Lubrication of precision instruments or motors always presents a highlyspecilalized and difllcult problem since the parts must be enclosed andthe lubricant cannot be renewed easily at frequent intervals, as iscustomary in common lubrication problems. In view of these factors, itis desirable to have a lubricant which will be non-volatile,non-corrosive, not subject to oxidation and, preferably, non-spreading.Since many delicate instruments are carried out of doors and, in modernmilitary operations, are exposed in aircraft to violent extremes intemperature, the selection and compounding of the lubricant to be usedon the many and minute bearing surfaces of delicate instruments isimmensely complicated by external temperature, pressure and humidityconditions. In addition to non-oxidizability and non-corrosiveness, lowviscosity at low temperature coupled with very small temperaturecoemcient of viscosity, good oiliness and extremely low volatility arenecessary.

It is the principal object of our invention to provide a lubricantcapable of giving satisfactory performance in all kinds of instrumentsor motors used in modern aircraft or ships or instruments used inscientific laboratories under the most exacting conditions oroperations.

It is a second object of our invention to characterize our lubricantsnot only by their capacity to perform but also by their composition,

Other objects and advantages of our invention will in part be obviousand in part appear hereinafter.

Our invention accordingly comprises the lubricating compositions havingthe properties and relation of components which will be exemplified inthe compositions hereinafter described and the scope of the inventionwill be indicated in the claims.

We have discovered that, in general, branched chain alkyl di-esters ofdicarboxylic aliphatic acids, such as the branched chain alkyl di-estersof dicarboxylic acids having from five to twelve carbon atoms permolecule, alone or as mixtures of two or more esters, possess at leasttwo desirable properties of good lubricants, namely, favorable viscositindicies, and low our points.

We have further discovered that a composition comprising essentially abranched-chain alkyl diester of azelaic acid, such as, di-(l-ethylpropyl) azelate, di-(butyl Cellosolve) azelate, di-(Z-ethyl hexyl)azelate, and di-(Z-ethyl butyl) azelate when properly compounded withcertain oxidation, rust and spreading inhibitors give remarkableperformance as lubricants in delicate instruments.

Our invention will be more clearly understood by reference to thefollowing table in which the properties of several lubricants of thisnew class, are summarized and by further reference to the examples inwhich the method of compounding lubncantmg compositions therefrom isdescribed:

Table Compound Property Temp. F

I II III IV Viscosity, Centi- 77 9. 62 13.9 17.4 11.5

stokes. 32 26. 0 39. i0 53. 0 30. 2

-4o 4. 25 1. 200 412 S 10 p e V 1 s c Temp. Curve (21p to -40) 0.79 0.700. 74 0.75

Specific Gravity 25/4" 0. 0.933 0.972

Surface Tensiom. 25 C. 28 29 Freezing Point.,

-7s -17 below -45 Neutralization Number (after evap.) 0.01 1. l2 Weightchange after evaporation 2 0. 34 0. 62 0.05 Per Cent Viscosity changeafter evaporation. 0. 6 2. 87

1 Key to table: I. di-(l-ethyl propyl) azelate L OzCHOOC(C 2)7COOCH( a6)2 b ii b ii eii b dcl ii fcoocmcmoc n III. di-(-e thyl liexy liazelate 7 nCiH CH C H5) CH OOC CH2)1COOCH3CH 0 H) (l H n IV. di-(2-ethylbutyl) azelate C2115) CHCH OOC CH 7COOCH2CH (C 11 2 Volatility or percent weight change after evaporation was measured by exposing a 10 gramsample of the fluid in an open dish having 16 square centimeters ofsurface area for 168 hours in a convection oven held at 150 F.

Although the pure esters described above have some of the essentialcharacteristics of good lubricants, they are not adaptable, as such, tolubricating problems for they are too readily oxidized and do notprotect the lubricated surfaces adequately against rusting under highhumidity conditions. We have found that certain substituted phenols andamines such as cyclohexyl phenol, para hydroxy diphenyl, 4-tertiarybutyl 2-phenyl phenol, p-hydroxy phenyl benzyl amine. thymol, andcatechol when added to the base lubricant in small quantities are goodoxidation inhibitors. They possess the valuable additional and essentialproperty of excellent compatibility with the base lubricant for they donot precipitate from the composition at temperatures as low as minus 40F.

We have found that polyvalent metallic soaps such as soaps of metals ofthe second group of the periodic table made from branched-chaincarboxylic acids having more than five carbon atoms in the chain whenadded to the base lubricant in small quantity are generally quiteefiective as rust or corrosion inhibitors. For example, small amounts ofzinc or calcium soaps of ethyl hexoic, phenyl stearic, phenoxy phenylstearic, xenyl stearic, xylyl stearic, phenyl undecylic, ethyl octanoicor phenyl acetic acids eflectively prevent rusting of lubricatedsurfaces.

The two types of soaps from the class indicated as being good rustinhibitors, that is, the zinc and calcium soaps, are exemplified by thefollowing compounds: zinc di-(2-ethvl hexoate), zinc di-(phenylstearate), zinc di-(phenoxy-phenyl stearate), zinc di-(xenyl stearate),zinc di-(xylyl stearate), zinc .di-(phenyl undecylate), zinc di-(4-ethyl octanoate), zinc di-(phenyl acetate), calcium di-2-ethylhexoate), calcium di-(phenyl stearate), calcium di- (phenoxy-phenylstearate),

calcium di-(xenyl stearate), calcium di-(xylyl stearate), calciumdi-(phenyl undecylate), calcium di-(4-ethyl octanoate), calciumdi-(phenyl acetate). These are especially advantageous in that they willnot precipitate from solution in the oil even after long exposure totemperatures of minus 40 F.

The oxidation and rust inhibitors of the classes mentioned above are notonly compatible with the base lubricant but are also mutually compatibleand are effective in the various di-esters even when used in very lowconcentrations. We have found, for example, that concentrations of 0.10%by weight of our oxidation inhibitors and 0.2% of our rust inhibitorsgive a satisfactory amount of protection. When the oxidation inhibitorsare used in relatively high concentrations,

for example, one-fourth to about one per cent by weight, their eflfectis prolonged because the excessive amount added creates a reserve in thecomposition. In general, we have found it best, as a conclusion fromexhaustive tests, to keep the concentration of inhibitors as low aspossible to obtain the desired degree of inhibitation.

of Example IV alter their viscosities desirably. In general, theireffect is to temperature curve in an upward direction with the efl'ectbeing more pronounced in the high temperature range than in the lowtemperature range. Thereby the temperature coeflicient of viscosity isdecreased to some extent.

The polymers mentioned above have the valuable property of remaining insolution when the lubricating composition comes into contact with apetroleum oil or solvent. This prevents serious cleaning difllcultiesfor, ordinarily, instruments are cleaned with petroleum solvents andshould a polymer thickener be precipitated by the petroleum solvent thehampered.

It is quite apparent that in compounding a? lubricant which in its finalform is to contain several additives, care must be displayed inselecting the compounds to be used to insure that they will be mutuallycompatible. Enough dif-' ferent oxidation and rust and inhibitors can befound in the general classes mentioned above so that mutually compatiblecompounds can be se-.

lected. The additives must be compatible not only at room temperaturebut over the entire range of temperature in which it is expected thelubricant will function to avoid their interaction or precipiation.

Each of the compositions described in the examples given below wassubjected to rust and oxidation stability tests. As a rust inhibitortest a sample of cold rolled steel was immersed in the composition andkept in contact with a drop of water for a period 01' 168 hours whilemaintained at a temperature 01' 140 F.

As an oxidation stability test, air was bubbled through a twenty-fivegram sample at a rate of twenty milliliters per minute for 168 hourswhile the composition was maintained at a temperature of 100 C. Samplesof copper, iron and Duralumin, each having a surface area of 1 squareinches were submerged in the samples of the compositions tested. Eachcomposition was further subjected to a bomb test in which twentyfivegrams of the composition having copper, iron and Duralumin samplessubmerged therein were held in a stainless steel bomb under a pure oxy-"gen pressure of 125 pounds per square inch for a period of 168 hours.

The stability was judged in each case by the freedom of the test samplefrom significant viscosity and neutralization number changes and freedomfrom corrosion of the metals submerged The volatility of the lubricantwill largely be determined by the volatility of the base compound. Fromthe figures given in the table, it is apparent that pure di-(l-ethylpropyl) azelate, di- (butyl Cellosolve) azelate and di- (ethyl hexyl)azelate are substantially involatile. Had the compounds tested beenappreciably impure. that is, bad they contained appreciable amounts ofthe alcohols and acids from which they were synthesized, theirvolatility according to the test used would have been considerablyhigher.

It is well known in the lubricating art that the viscositycharacteristics 01' a lubricant can be adjusted by dissolving therein apolymer thickener. We have found that small amounts of the polyalkylesters of acrylic acid such as the Acryloid resins (F10, HF845, HF880,products of Rohm and Haas and Co.) and polymers such as polybutenesdissolved in the lubricating compositions in the sample.

The compounding of lubricating compositions according to our inventionwill be more readily understood by reference to the following examples:

Example I Base lubricant-" di-(2-ethyl hexyl) azelate Rust inhibitor 025(wt.) zinc di-(xylyl steal-ate) Oxidation inhibit oi 020% (wt.)4-tertiary butyl 2-phenyl phenol The compositions when tested forlubricating.

quality gave outstanding performance in the bearings of gyro compasses,clocks, and small synchro motors such as are used in fire control equipment. Its viscosity-temperature curve corresponds, within experimentalerror when it is prepared from the pure compound, to that of the purecompound. It was non-corrosive and stable as determined by the testsindicated above.

The above composition was clear and substantially water white before thetests; additives give a slight color to the compositions. It remaineddisplace the viscosityprocess would be seriously.

clear and substantially water white and free of precipitate after testeven when stored at minus 65 F.

Example II Baselubricani; di-(butyl Cellosolve) azelate Bustinhlbitor0.25t% (:vty) calcium di-(plienyl a cam e Oxidation inhibitor"--. 0.2%(wt.) diphenyl amine The composition when tested for lubrication qualitygave outstanding performance, comparable to that of the composition ofExample I. Its viscosity temperature curve corresponds, withinexperimental error when it is prepared from the pure compound, to thatof the pure compound. It was colorless, non-corrosive and stable asdetermined by the tests outlined above and in Example I.

Example III Example IV Base lubricant di-(2-ethyl butyl) azelate Rustinhibitor 0.25% (wt.) calcium di-(phenyl undecylate) Oxidation inbibitor0.20% (wt.) cyclohexyl phenol The composition when tested forlubricating quality gave excellent performance in the bearings ofvarious aeronautical, navi ation and ordnance instruments. Itsviscosity-temperature curve corresponds, within experimental error whenit is prepared from the pure compound, to that of the pure compound. Itwas non-corrosive and stable as determined by the tests outlined aboveand in Example I.

Since various changes may be made in the above compositions by changingconcentrations and combinations of additives and by mixing esters asbase lubricants, thus making compositions different from those in theexamples but coming within the scope of our invention, it is intendedthat all matter contained in the above table, description and examplesshall be interpreted as illustrative and not in a limiting sense. It isalso to be understood that the following claims are intended to coverall the generic and specific features of the invention which, as amatter of language, might be said to fall therebetween.

The invention described herein may be manufacured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalty thereon or therefor.

Having described our invention, what we claim as new and desire tosecure by Letters Patent of the United States is:

1. A fluid ester lubricating composition, consisting essentially of,di-(Z-ethylhexyl) azelate having dissolved therein about 0.1 to about1.0 per cent by weight of zinc di-(xylylstearate) as a rust inhibitorand about 0.1 to about 1.0% by weight of 4-tertiary butyl 2-phenylphenol as an oxidation inhibitor.

2. A fluid ester lubricating composition, consisting essentially of, asthe base lubricant, di- (Z-ethyl butyl) azelate blended with rust andoxidation inhibiting proportions, respectively, of a polyvalent metalsoap of a substituted fatty acid as a rust inhibitor and a substitutedphenolic compound as an oxidation inhibitor.

3. A fluid ester lubricating composition, consisting essentially of, asthe base lubricant, di- (l-ethyl propyl) azelate blended with rust andoxidation inhibiting proportions, respectively, of a polyvalent metalsoap of a substituted fatty acid as a rust inhibitor and a substitutedphenolic compound as an oxidation inhibitor.

A fluid ester lubricating composition, consisting essentially of, as thebase lubricant di- (2-ethyl butyl) azelate and having dissolved thereinabout 0.1% to 1.0% by weight of calcium di-(xylyl stearate) as rustinhibitor and about 0.1% to 1.0% by weight of 4-tertiary butyl-2- phenylphenol as an oxidation inhibitor.

5. A fluid ester lubricating composition consisting essentially of, asthe base lubricant di- (l-ethyl propyl) azelate having dissolved thereinabout 0.1% to 1.0% by weight of calcium di- (xylyl stearate) as a rustinhibitor and about 0.1% to 1.0% by weight of 4-tertiary butyl-2- phenylphenol as an oxidation inhibitor.

6. A fluid ester lubricating composition, consisting essentially of, asthe base lubricant, a branched-chain, lower alkyl di-ester of azelaicacid blended with rust and oxidation inhibiting proportions,respectively, of a polyvalent metal soap of a saturated fatty acidsubstituted by an organic radical selected from the group consisting ofaryl and alkylaryl radicals as a rust inhibitor and a phenolic compoundsubstituted by an organic radical selected from the group consisting ofaryl, alkyl, alkylaryl and amino radicals as an oxidation inhibitor.

'7. A fluid ester lubricating composition consisting essentially of, asthe base lubricant, di- (Z-ethylhexyl) azelate blended with rust andoxidation inhibiting proportions, respectively, of a polyvalent metalsoap of a saturated fatty acid substituted by an organic radicalselected from the group consislting of aryl and alkylaryl radicals as arust inhibitor and a phenolic compound substituted by an organic radicalselected from the group consisting of aryl. alkyl, alkylaryl and aminoradicals as an oxidation inhibitor.

8. A fluid ester lubricating composition, consisting essentially of, asa base lubricant di-(2- ethyl hexyl) azelate blended with rust andoxidation inhibiting proportions, respectively, of a polyvalent metalsoap of a saturated fatty acid substituted by an organic radicalselected from the group consisting of aryl and alkylaryl radicals as arust inhibitor, 9. phenolic compound substituted by an organic radicalselected from the group consisting of aryl, alkyl, alkylaryl and aminoradicals as an oxidation inhibitor and a polymer thickener.

WILLIAM A. ZISMAN. CHARLES M. MURPHY, Ja. JOHN K. WOLFE.

REFERENCES CITED The following references are of record in the

3. A FLUID ESTER LUBRICATING COMPOSITION, CONSISTING ESSENTIALLY OF, ASTHE BASE LUBRICANT, DI(1-ETHYL PROPYL) AZELATE BLENDED WITH RUST ANDOXIDATION INHIBITING PROPORTIONS, RESPECTIVELY, OF A POLYVALENT METALSOAP OF A SUBSTITUTED FATTY ACID AS A RUST INHIBITOR AND A SUBSTITUTEDPHENOLIC COMPOUND AS AN OXIDATION INHIBITOR.